Optical communication systems may generally be classified into two detection types known as direct detection and coherent detection. In a direct detection system, data may be modulated using either the magnitude or the phase of the optical signal. In a coherent detection system, data may be modulated using both the magnitude and the phase of the signal, thus allowing greater data transmission rates. As the demand for higher transmission rates increases, data streams may also be modulated using multiple polarizations of optical signals. However, optical signals passing through optical channels are often distorted due to chromatic dispersion, polarization dependent impairment, noise, differential group delay, state of polarization (SOP) rotation, etc. Such distortion may affect the reception of the polarized optical signals and may increase the difficulty in distinguishing between different polarized optical signals.
In what is known as an Intensity Modulation Directly Detected (IMDD) system, distortion may be minimized with a dispersion compensation module (DCM) and polarization control devices, which may compensate corresponding distortions and recover signals. However, as optical communication systems move to higher baud rate requirements, signal quality tends to become more sensitive to distortion, which makes it difficult to recover signals using conventional methods.